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Limit State (limit + state)
Selected AbstractsZur Ermittlung der Normalkraft-Verlängerung und Moment-Krümmung-Beziehungen der Stahlbetonbauteile im Grenzzustand der GebrauchstauglichkeiBETON- UND STAHLBETONBAU, Issue 8 2009Eugen Du, ulescu Dr.-Ing. Berechnungs- und Bemessungsverfahren; Normen, Vorschriften, Richtlinien Abstract Die Nachweise zur Begrenzung der Verformungen von Stahlbetonbauteilen sind infolge der Verwendung von Baustoffen höherer Festigkeiten immer wichtiger geworden, oft sogar maßgebend. Eine Verdopplung der Betondruckfestigkeit eines normalen Betons ruft eine etwa 20%ige Erhöhung des Ec -Moduls hervor aber keine des Betonstahls, da Es konstant ist. Dies und die dementsprechend schlanker gewordenen Stahlbetonbauteile führen zu größeren Verformungen , Verlängerungen, Durchbiegungen und/oder Verdrehungen , die deren Verhalten beeinträchtigen können. Die für die Ermittlung der Verformungen benötigten "Normalkraft-mittlere Dehnungslinien", bzw. "Moment-mittlere Krümmungslinien" werden erläutert. About the Calculation of Displacements of Reinforced Concrete Members in the Serviceability Limit State The verification of reinforced concrete elements for the purpose of limiting deformations has become increasingly important, often even decisive, as a result of the use of higher strength materials. A doubling of the compressive strength of a normal concrete causes an increase of about 20% in the Ec -module, and none of reinforcing steel, because Es is constant. This and, accordingly, the slender reinforced concrete elements lead to larger deformations , elongations, deflections and/or rotations , which may affect their behaviour. The determination of "axial tensile force , mean strain diagrams", respectively "bending moment , mean curvature diagrams", needed for the calculation of the displacements, is explained. [source] A Risk-Cost Optimized Maintenance Strategy for Corrosion-Affected Concrete StructuresCOMPUTER-AIDED CIVIL AND INFRASTRUCTURE ENGINEERING, Issue 5 2007Chun-Qing Li It is also observed that some severely deteriorated concrete structures survive for many years without maintenance. This raises the question of why and how to maintain corrosion-affected concrete structures, in particular in the climate of an increasing scarcity of resources. The present article attempts to formulate a maintenance strategy based on risk-cost optimization of a structure during its whole service life. A time-dependent reliability method is employed to determine the probability of exceeding a limit state at each phase of the service life. To facilitate practical application of the formulated maintenance strategy, an algorithm is developed and programmed in a user-friendly manner with a worked example. A merit of the proposed maintenance strategy is that models used in risk assessment for corrosion-affected concrete structures are related to some of the design criteria used by practitioners. It is found in the article that there exists an optimal number of maintenances for cracking and delamination that returns the minimum total cost for the structure in its whole life. The maintenance strategy presented in the article can help structural engineers, operators, and asset managers develop a cost-effective management scheme for corrosion-affected concrete structures. [source] Seismic collapse risk of precast industrial buildings with strong connectionsEARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 8 2010Miha Kramar Abstract A systematic seismic risk study has been performed on some typical precast industrial buildings that consists of assemblages of cantilever columns with high shear-span ratios connected to an essentially rigid roof system with strong pinned connections. These buildings were designed according to the requirements of Eurocode 8. The numerical models and procedures were modified in order to address the particular characteristics of the analyzed system. They were also verified by pseudo-dynamic and cyclic tests of full-scale large buildings. The intensity measure (IM)-based solution strategy described in the PEER methodology was used to estimate the seismic collapse risk in terms of peak ground acceleration capacity and the probability of exceeding the global collapse limit state. The effect of the uncertainty in the model parameters on the dispersion of collapse capacity was investigated in depth. Reasonable seismic safety (as proposed by the Joint Committee on Structural Safety) was demonstrated for all the regular single-storey precast industrial buildings addressed in this study. However, if the flexural strength required by EC8 was exactly matched, and the additional strength, which results from minimum longitudinal reinforcement, was disregarded as well as large dispersion in records was considered, the seismic risk might in some cases exceed the acceptable limits. Copyright © 2009 John Wiley & Sons, Ltd. [source] Seismic reliability of V-braced frames: Influence of design methodologiesEARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 14 2009Alessandra Longo Abstract According to the most modern trend, performance-based seismic design is aimed at the evaluation of the seismic structural reliability defined as the mean annual frequency (MAF) of exceeding a threshold level of damage, i.e. a limit state. The methodology for the evaluation of the MAF of exceeding a limit state is herein applied with reference to concentrically ,V'-braced steel frames designed according to different criteria. In particular, two design approaches are examined. The first approach corresponds to the provisions suggested by Eurocode 8 (prEN 1998,Eurocode 8: design of structures for earthquake resistance. Part 1: general rules, seismic actions and rules for buildings), while the second approach is based on a rigorous application of capacity design criteria aiming at the control of the failure mode (J. Earthquake Eng. 2008; 12:1246,1266; J. Earthquake Eng. 2008; 12:728,759). The aim of the presented work is to focus on the seismic reliability obtained through these design methodologies. The probabilistic performance evaluation is based on an appropriate combination of probabilistic seismic hazard analysis, probabilistic seismic demand analysis (PSDA) and probabilistic seismic capacity analysis. Regarding PSDA, nonlinear dynamic analyses have been carried out in order to obtain the parameters describing the probability distribution laws of demand, conditioned to given values of the earthquake intensity measure. Copyright © 2009 John Wiley & Sons, Ltd. [source] Seismic performance of a 3D full-scale high-ductile steel,concrete composite moment-resisting frame,Part II: Test results and analytical validationEARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 14 2008A. Braconi Abstract This paper presents the results of a multi-level pseudo-dynamic seismic test program that was performed to assess the performance of a full-scale three-bay, two-storey steel,concrete composite moment-resisting frame built with partially encased composite columns and partial-strength beam-to-column joints. The system was designed to develop a ductile response in the joint components of beam-to-column joints including flexural yielding of beam end plates and shear yielding of the column web panel zone. The ground motion producing the damageability limit state interstorey drift caused minor damage while the ultimate limit state ground motion level entailed column web panel yielding, connection yielding and plastic hinging at the column base connections. The earthquake level chosen to approach the collapse limit state induced more damage and was accompanied by further column web panel yielding, connection yielding and inelastic phenomena at column base connections without local buckling. During the final quasi-static cyclic test with stepwise increasing displacement,amplitudes up to an interstorey drift angle of 4.6%, the behaviour was ductile although cracking of beam-to-end-plate welds was observed. Correlations with numerical simulations taking into account the inelastic cyclic response of beam-to-column and column base joints are also presented in the paper together. Inelastic static pushover and time history analysis procedures are used to estimate the structural behaviour and overstrength factors of the structural system under study. Copyright © 2008 John Wiley & Sons, Ltd. [source] Shear and objective stress rates in hypoplasticityINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 9 2003D. Kolymbas Abstract This paper addresses some questions referring to shear within the context of hypoplasticity and the importance of objective stress rates in constitutive modelling. A short introduction to the stress changes due to rotations is followed by a discussion of the merits of the individual objective stress rates. It is shown that many of them differ only by terms that pertain to the constitutive description of a material. Apart from this it is shown that the Zaremba,Jaumann stress rate can lead to inconsistencies. This is, however, rather of academic importance and it appears that the use of , instead of any objective stress rate produces only minor or even undiscernible errors. Finally, a question referring to limit states is addressed, which is of particular interest with respect to hypoplasticity: should the limit state be defined by ,=0 or by T,=0? Copyright © 2003 John Wiley & Sons, Ltd. [source] An unconditionally convergent algorithm for the evaluation of the ultimate limit state of RC sections subject to axial force and biaxial bendingINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 8 2007G. Alfano Abstract We present a numerical procedure, based upon a tangent approach, for evaluating the ultimate limit state (ULS) of reinforced concrete (RC) sections subject to axial force and biaxial bending. The RC sections are assumed to be of arbitrary polygonal shape and degree of connection; furthermore, it is possible to keep fixed a given amount of the total load and to find the ULS associated only with the remaining part which can be increased by means of a load multiplier. The solution procedure adopts two nested iterative schemes which, in turn, update the current value of the tentative ultimate load and the associated strain parameters. In this second scheme an effective integration procedure is used for evaluating in closed form, as explicit functions of the position vectors of the vertices of the section, the domain integrals appearing in the definition of the tangent matrix and of the stress resultants. Under mild hypotheses, which are practically satisfied for all cases of engineering interest, the existence and uniqueness of the ULS load multiplier is ensured and the global convergence of the proposed solution algorithm to such value is proved. An extensive set of numerical tests, carried out for rectangular, L-shaped and multicell sections shows the effectiveness of the proposed solution procedure. Copyright © 2007 John Wiley & Sons, Ltd. [source] Monopilegründungen von Offshore-Windenergieanlagen , Zum Ansatz der BettungBAUTECHNIK, Issue 1 2005Jürgen Grabe Univ.-Prof. Bei der Gründung von Offshore-Windenergieanlagen mit Monopiles stellt die große Momenten- und Horizontalkraftbelastung und deren zyklisches Auftreten eine besondere Herausforderung an die Prognose der Pfahlverformungen dar. Für ein System mit beispielhaften Abmessungen, Baugrundverhältnissen und Belastungen werden die konventionellen Verfahren zur Berechnung der horizontalen Pfahltragfähigkeit und -verformung, Bettungsmodulverfahren und API-Verfahren, mit den Ergebnissen einer 3D-FE-Analyse verglichen. Es zeigt sich, daß die konventionellen Verfahren für die Prognose der Verformungen im Gebrauchszustand, also deutlich unterhalb der Grenzlast, für dieses Beispiel unzureichend sind. Die Verteilung des Bettungsmoduls über die Tiefe wird mit keinem der Verfahren zutreffend abgebildet. Des weiteren wird die Veränderung des Bettungsmoduls über mehrere Zyklen für Schwell- und Wechselbelastungen untersucht. Vor allem bei einer Schwellast wird der auf den Ausgangszustand bezogene Bettungsmodul mit jedem Zyklus verändert. Die Verschiebung des Pfahlkopfs steigt auch nach 20 Belastungszyklen noch an. Der aus der ödometrischen Steifigkeit des Bodens abgeleitete Bettungsmodul ist zur Prognose der Pfahlverformungen insbesondere bei zyklischer Last fragwürdig. Hierfür besteht insbesondere in Anbetracht der geplanten Investitionen erheblicher Forschungsbedarf. Monopile foundations for Offshore-Wind Power Plants , approach of subgrade reaction. The large moments and horizontal forces and their cyclic occurrence represent a special challenge to the prognosis of the deformations of Monopiles as a foundation of offshore wind energy plants. The conventional procedures for the computation of the horizontal pile bearing capacity and deformation, subgrade reaction procedure and API procedure, are compared with the results of a 3D-FE analysis for a system with exemplary dimensions, soil conditions and loads. It is shown that the conventional procedures for the prognosis of the deformations in the serviceability limit state, thus clearly underneath the maximum load, for this example are insufficient. The distribution of the subgrade reaction modulus over the depth is sufficiently approximated with none of these procedures. Moreover the change of the subgrade reaction modulus is investigated for several cycles swelling and alternated loads. The modulus of subgrade reaction, referred to the initial pile position, changes especially under swelling loads for each loading cycle. The displacement of the pilehead still increases after 20 cycles. The modulus of subgrade reaction derived from the oedometric soil stiffness does not produce an accurate prognosis of the pile deformation particularly for cyclic loads. For this purpose further investigations are necessary. [source] Anwendung von Trapezblechstegen im BrückenbauBETON- UND STAHLBETONBAU, Issue 9 2009Längsschubtragverhalten von Betondübeln in Kombination mit Trapezblechstegen Brückenbau; Entwurf und Konstruktion Abstract Trapezblechstege im Brückenbau kommen trotz der großen Vorteile, die diese Bauweise bietet, in Deutschland bisher nur an einem Pilotprojekt zur Anwendung. Durch die charakteristischen Eigenschaften des Trapezbleches entstehen konstruktive und wirtschaftliche Vorteile gegenüber herkömmlichen Brückenbauweisen. Allerdings lassen die aktuell gültigen Regelwerke aufgrund fehlender Kenntnis zum Tragverhalten und mangelnder Erfahrung keine wirtschaftliche Ausbildung zu. Dies zeigt sich am Beispiel des Pilotprojekts. Die Ausbildung der Verbundfuge wurde hier nur sehr unbefriedigend gelöst und verdeutlicht somit die Notwendigkeit einfacher und praktikabler Verbindungsmöglichkeiten. Am Institut für Leichtbau Entwerfen und Konstruieren der Universität Stuttgart wurde in Zusammenarbeit mit dem Institut für Konstruktion und Entwurf ein von der Forschungsvereinigung für Stahlanwendung e. V. (FOSTA) finanziertes Forschungsvorhaben bearbeitet, bei dem unterschiedliche Verbundfugenausbildungen numerisch und experimentell untersucht wurden. Der folgende Beitrag beschränkt sich auf die Verwendung von Betondübeln als Verbundmittel und stellt hierfür ein einfaches Bemessungskonzept für die Verbundsicherung unter Längsschubbeanspruchung im Grenzzustand der Tragfähigkeit vor. The use of corrugated steel webs in bridge constructions , Load bearing behaviour of concrete dowels in combination with corrugated steel webs under longitudinal shear Studies of the load bearing behaviour under shear force of integrated connections at composite bridge girders using corrugated steel webs. Up to now there is only one project in Germany, where the application of corrugated steel webs has been practiced in the field of composite bridges. Due to the characteristics of the corrugated steel web this construction method has constructive and economic advantages. However there is a lack of experiences and standards to fully utilize these advantages and to allow an economic application. Especially the first project in Germany expose some critical points. The design of the joint between the concrete slab and the corrugated steel web is actually not satisfactory and shows the need for simpler and more practicable connection methods. At the Institute for Lightweight Structures and Conceptual Design at Universität Stuttgart and together with the Institute of Structural Design, a research project, financed by Forschungsvereinigung für Stahlanwendung e. V. (FOSTA) was made. Within this project different types of composite joints were experimentally and numerically analysed. This paper deals only with the investigations of concrete dowels as connectors. On the basis of these studies simple design rules for shear connection in the ultimate limit state were developed. [source] | |||||||||||||||||||